1. Field of the Invention
The present invention relates to a press apparatus used for magnetic injection molding machines, and more particularly to a press apparatus of the vertical type using a movable table.
2. Prior Art of the Invention
In a conventional press apparatus for magnetic injection molding machines of the vertical type using a movable table such as a rotary table and a slide table, there are three types of the press apparatus used for magnetic injection molding machines. The first type has a metal mold surrounded by an annular magnetic coil for producing magnetic flux, the second type has a press surrounded by an annular magnetic coil for producing magnetic flux and the third type has a platen surrounded by an annular magnetic coil for producing magnetic flux.
In the case of the first type, it is necessary to provide the magnetic coil not only at the upper metal mold but also the lower metal mold mounted on a movable table, therefore the wiring of wires for supplying electric power to the coil movable together with the movable table becomes very complex and further it becomes undesirably necessary to provide a plurality of coils of equinumber to the number of the lower metal molds provided on the movable table thereby increasing the cost of the injection molding machine. In the case of the second type, the whole dimension of an injection molding machine becomes bulky and complex and it is necessary to move the magnetic coils by using hydraulic equipment exclusively used for moving the magnetic coils whenever a molded work piece is removed from the metal mold. Furthermore, it is necessary to use an expensive non-magnetic steel for tie bars in order that the tie bars disposed at the inner side of the magnetic coil do not serve to form a portion of a magnetic circuit.
The above mentioned drawbacks are eliminated in the case of third type, as shown in FIG. 6, in which annular magnetic coils 54 and 56 are respectively disposed at the periphery portion of the projected portions 50a and 52a of an upper metal mold 50 and a lower metal mold 52. In the case of a rotary table 58 made of ferromagnetic material, however, there is undesirably produced a magnetic circuit having the magnetic flux flow passing through the rotary table 58, the projected portion 52a and the lower metal mold 52 as shown by an arrow 60 in FIG. 6, thereby undesirably decreasing the magnetic flux to be utilized for the upper and lower metal molds. Furthermore, in the case of the rotary table 58 made of non-magnetic material, the flow of the magnetic flux is undesirably reduced by the non-magneteic rotary table 58 thereby increasing the magnetic resistance or reluctance of the magnetic circuit and decreasing the efficiency of the magnetic field.